Modular alternating to direct current converter with extruded corner housing portions

ABSTRACT

A modular power supply for converting three-phase alternating to direct current for high power applications. A plurality of individual rectifying modules are all fed through a common threephase SCR controller. Each module in turn comprises its own transformer and rectifying circuit and has associated therewith an individual circuit breaker and cooling fan. The DC output from each module is collected by a common bussing arrangement and a particular automatic voltage-current regulator is provided to control the duty cycle of the common SCR controller. The current feedback includes a plurality of resistors that are selectively connected in the feedback circuit according to the number of modules in the power supply so that effective regulation is achieved regardless of the number of modules included. The module packaging is substantially the same with both modules used for high voltage, low current applications and for low voltage, high current applications. The construction of the modules is such as to facilitate interchangeability of many of the parts between the high voltage and low voltage module.

United States Patent [72] lnventors Thomas N. Urquhart y; Michael A.Koltunick. Warren; Robert (1'. Plantholt, Rochester, all of. Mich.

[211 Appl. No. 9,294

[22] Filed Feb. 6, 1970 [45] Patented June 22, 1971 [73] AssigneeControlled Power Corporation Farmington, Mich.

[541 MODULAR ALTERNATING 'IO DIRECT CURRENT CONVERTER WITII EXTRUDEDCORNER HOUSING PORTIONS 15 Claims, 13 Drawing Figs.

[52] U.S.Cl 317/100,

[51] Int. Cl 1102b 1/18 [50] Field ofSearch 174/15 R,

[56] References Cited UNITED STATES PATENTS 2,171,643 9/1939 Brenkert317/100 3,355,540 11/1967 Newell 317/100 X Assistant Examiner-Gerald P.Tolin Att0rneyBarnes', Kisselle, Raisch and Choate ABSTRACT: A modularpower supply for converting threephase alternating to direct current forhigh power applications. A'plurality of individual rectifying modulesare all fed through a common three-phase SCR controller. Each module inturn comprises its own transformer and rectifying circuit and hasassociated therewith an individual circuit breaker and cooling fan. TheDC output from each module is collected by a common bussing arrangementand a particular automatic voltage-current regulator is provided tocontrol the duty cycle of the common SCR controller. The currentfeedback includes a plurality of resistors that are selectivelyconnected in the feedback circuit according to the number of modules inthe power supply so that effective regulation is achieved regardless ofthe number of modules included. The module packaging is substantiallythe same with both modules used for high voltage, low currentapplications and for low voltage,

high current applications. The construction of the modules is such as tofacilitate interchangeability of many of the parts between the highvoltage and low voltage module.

PATENTFQD- June? IS'H sum 1 OF 5 5 rb scR CONT ROLLER MICHAEL A.KOLTUNIAK ROBERT G. PLANT ATTORNEYS INVIENTIORS i ATTORNEYS SHEET 2 [IF5 PATENTEDJUHMZZ [911 THOMAS N.URQUHART MICHAEL A. KOLTUNIAK BY ROBERTc. PLANTHOLT M z ms T M PATENTED JUN22|97| SHEET 3 BF 5 INVENTORS THOMASN. URQUHART MICHAEL A. KOLTUNIAK BY ROBERT c. PLANTHOLT ATTORNEYSPATENTEUJUH22IB7I 3586315 sumuurs me an a T165 //4,//6 z lNVENTORSTHOMAS N. URQUHART MICHAEL A. KOLTUNIAK BY ROBERT c. PLANTHOLT T168ATTORNEYS PmEmtn zzl ri 3586915 SHEET 5 [IF 5 [Ir/111111111 Z5 T161 277INVENTORS' THOMAS N.URQUHART MICHAEL A. KOLTUNIAK BY ROBERT G. PLANTHOLTMWWPM ATTORNEYS shipping, handling, installation and repair; thatachieves effecl tive interchangeability between different modules of thesame power handling capabilities as well as utilizing many common partsas between modules for different power handling capabilities; and thatprovides a lightweight and compact modular power supply by comparisonwith prior art power supplies.

Other objects, features and advantages of the present invention willbecome apparent in connection with the following description, theappended claims and the accompanying drawings in which:

FIG. I is a front elevational view of an altemating-to-direct currentconverter having a modular construction according to the presentinvention consisting of 21 individual modules;

FIG. 2 is a functional block diagram for a modular power supply of thepresent invention and is illustrated for only three modules for purposesof simplicity;

FIG. 3 is a schematic circuit diagram for the maincontroller-transformer-rectifying circuit paths of the powersupplyillustrated in FIG. 2;

FIG. 4 is a schematic circuit diagram showing the details of avoltage-currentregulation circuit of FIGS. 2 and 3;

FIG. 5 is a top plan view of a single module used for high voltageapplications;

FIG. 6 is a side view of the module illustrated in FIG. 5;

FIG. 7 is an exploded fragmentary view of one side of the moduleillustrated in FIG. 5;

FIG. 8 is a fragmentary perspective view illustrating a complete moduleand its associated circuit breaker;

FIG. 9 is an enlarged fragmentary view from FIG. I illustrating a singlemodule and its associated circuit breaker;

FIG. 10 is a top plan view of a modified module for low voltageapplications;

FIG. 11 is a side view of the module illustrated in FIG. 10;

FIG. I2 is an exploded fragmentary view illustrating the construction ofthe side panels for the embodiment illustrated in FIG. 10; and

FIG. 13 is a front elevational view of the modification of FIG. 10 witha portion broken away to better illustrate the heat sink.

Referring more particularly to FIG. I, there is illustrated a modularpower supply 30 of the present invention generally comprising a bank 32of 21 individual rectifying modules 34 and a cabinet 35 which houses thecontroller circuits for the bank of modules. The 21 modules are arrangedin three vertical columns, each column consisting of seven modules.'Associated with each module is a separate circuit breaker 36. Each ofthe individual modules 34 is substantially identical, both in mechanicalconstruction and electrical circuitry. Similarly, for purposes ofunderstanding the present invention utilizing a plurality of modules,supplied from a common input bus and supplying a common output bus, itwell be apparent that the operation and construction is basically thesame regardless of the number of modules 34 utilized. Hence for purposesof illustration, the functional block diagram of FIG. 2 illustrates asimplified modular power supply incorporating only three modules,designated 34a, 34b and 340. For purposes of clarity, the correspondingcircuit breakers 36a, 36b, 36c are illustrated enclosed in the dashedline indicating an individual module, although it will be understoodthat the circuit breakers 36 are physically separated from otherelectrical components in the associated module 34 as will later bedescribed in greater detail. 7

Referring more particularly to FIG. 2, a three-phase source 40 isconnected by lines 42 to a main circuitbreaker 44 to a three-phase SCRcontroller 46. The output of controller 46 is in turn fed via parallelpaths through the respective modules 34a--c to the common DC outputbusses 48, 50. Each of the parallel paths through a respective module34a, 344b, and 34c is through the associated circuitbreaker 36 and adelta-to-wye transformer 52 which feeds a three-phase diode rectifyingcircuit 54. The output from the three rectifying circuits 54 areconnected in parallel to the output buses 48, 50.

Controller 46 is a full-wave, duty cycle controller that receives sixindividual gating signals from an SCR firing circuit 58 which in turn isenergized from the three-phase input lines 42. Firing circuit 58 has acontrol input at 60 that receives a DC feedback control signal from thevoltage-current regulation circuit indicated generally at 62. Thecontrol signal at 60 controls the angular position of the various gatingsignals from circuit 58 relative to the phase angles of the positive andnegative half cycles in each of the three phases at controller 46.Stated differently, the control signal 60 determines the duty cycle ineach of the phases at controller 46 to thereby regulate the powersupplies to the modules 34.

In general, the DC control signal at 60 is derived from either a voltagelevel at busses 48,50 or the current level at busses 48, 50. Moreparticularly, the voltage across busses 48, 50 is applied through asuitable isolating resistor 66 across a summing resistor 68 to developthe output signal at the summing terminal 70 that forms one inputtenninal of the NOR gate 72. A voltage reference from source 74 is alsoapplied through an isolating resistor 76 across summing resistor 68 andin bucking relation to the-feedback voltage through resistor 66 suchthat the output signal developed at the summing terminal 70 has a valueindicating whether the reference is greater or less than the feedbackfrom busses 48, 50 in addition to indicating the amount of deviationtherebetween. Similarly, the output current-in the positive bus 50 issampled by the shunt 80 and thecurrent feedback signal is fed through aDC amplifier 82, a chopper 84, an output driver amplifier 86 to arectifier-filter circuit 88 that develops a DC signal representing themagnitude of the current in lines 48, 50. The signal developed bycircuit 88 isapplied through an isolating resistor 90 across a summingresistor 92. Equal portions 90a, 90b, 90c of resistor 90 are arranged tobe shorted by respective contacts 94a, 94b, 94c. Contacts 94a, 94b, 940are operated by the respective circuit breakers 36a, 36b, 360 so thatwhen the circuit breakers are closed their corresponding contacts 94 areopened. As will later be explained in greater detail, should one of thecircuit breakers open, for example, circuit breaker 36a, thecorresponding contact 94a will be closed to short out resistor 90a andincrease the feedback applied to the summing resistor 92 from the shunt80. A current reference signal from source 98 is also applied across thesumming resistor 92 through an isolating resistor 100 in buckingrelation to the current feedback signal from circuit 88 so that theoutput developed at the summing terminal 102 has an amplitude thatindicates which of the two signals exceeds the other as well as theamount of difference between the signals applied across resistor 92. Thesignal developed at the summing point 102 is applied to the other inputof the NOR gate 72.

The circuit details of the SCR controller 46, the modules 34, togetherwith start-stop circuitry and the fan motor circuitry for cooling themodules 34 is shown in greater detail in FIG. 3 whereas the circuitdetails of the voltage-current regulating circuits 62 are shown ingreater detail in FIG. 4. Referring more particularly to FIG. 3, thethree-phase lines 42 are fed through the circuit breaker 44 to the SCRcontroller 46. Each of the three-phase lines is connected to the circuitbreakers 36 through a pair of silicon controlled rectifiers 110, 111 forone of the lines, 111 for a second of the lines and 110", 111" for forthe third line. Since the construction and operation of a three-phase,full-wave duty cycle controller is known, per se, for purposes ofsimplicity only one of the SCRs 110 is shown with its gate circuitconnected to the regulating circuit 62. It will be understood that inFIG. 3, the SCR firing circuit 58 (FIG. 2) has been omitted as aseparate element and, for purposes of simplicity, included within theregulation circuit 62. Hence as will be apparent, in accordance with oneimportant aspect of the present invention, the controller 46 iseffective to simultaneously control the power applied to the respectivecircuit breakers 36a, 36b, 360 to the primary winding 114ac of the threetransformers 52ac. It should be noted that transformers 52 have theirprimaries 114 connected in a delta and their secondaries 116 wyeconnected in the preferred embodiment. It has beenfound with the modularcircuit being described, a delta-delta transformer and a wye-wyetransformer do not operate as effectively for a given physical size dueto poorer transformer efficiency. It has also been found that awye-delta transformer creates phasing problems at the SCR controller 46.The secondaries 116 feed the rectifying circuits 54, each of whichconsists of six diode rectifiers connected in the three-phase, full-wavebridge circuit illustrated.

The start-stop circuit 120 is fed from one phase of the threephase inputat lines 42 via a control transformer 122 which steps down the 480 voltsacross the single-phase input to 115 volts for the circuit 120.Connected across the secondary of transformer 122.is a pilot lightl24.-A control relay RLM is arranged to be connected across thesecondary of transformer '122 through a normally closed stop switch 126and a normally opened start switch 128. Relay RLM has two normally opencontacts IRLM and 2RLM. When start switch 128 is closed to energizerelay RLM, the contacts 2RLM close to seal relay RLM and contacts IRLMclose to provide the power for the regulating circuit 62 which includesthe SCR firing circuit 58 and for the fan motors 130 that cool the SCRsin the controller 46. For purpose of simplicity, in the presentapplication, a control relay is designated by a letter designation andthe contacts operated by the relay will be designated by the same letterdesignation preceded by a numeral designation. Substantially the sameconvention will be utilized for identifying solenoids and the contactsassociated therewith. A separate pilot light 134 is connected acrossrelay RLM toprovide a separate indication that the power to the circuit62 is A solenoid CBM is also arranged to be connected across thesecondary of transformer 122 to an emergency stop switch 136. SolenoidCBM is part of the circuit breaker 44 and is arranged to open the maincircuit breaker 44 in response to closure of the emergency stop switch136.

Two of the main lines 42 also feed a second stepdown control transformer140 which is arranged to energize the circuit 142 that controls themotors for respective fans in each of the modules 34. Circuit 142 isalso arranged to disconnect a module in response to excessivetemperatures at the heat sink for the diode rectifiers 54. Moreparticularly, a control relay RLA connected directly across thesecondary of transformer 140 has a normally closed contact lRLA in thecircuit 120. When transformer 140 is energized to in turn energize relayRLA, contacts lRLA open so that a time delayed closing of contacts lRLMdoes not cause solenoid CBM to be energized. If, however, the power tocircuit 142 is lost, as by a fuse blowing, relay RLA is deenergized andcontacts 1RLA close to energize solenoid CBM through the contacts IRLMthat are closed in response to energization of relay RLM. This operatesto open the main circuit breaker 44 to disconnect the entire powersupply 30 from the lines 42. When the main circuit breaker 44 is openedbythe solenoid CBM, either by operation of the emergency stop switch 136or closure of contacts lRLA and lRLM, the power to the power supply 30can be reconnected only by manual closure of the main circuit breaker44.

The circuit 142 also includes fan energizing and temperature overloadcircuits 1440, 144b, and 1440 for the modules 34a, 34b, 34c,respectively. Since the circuits 144 are substantially identical, anunderstanding of the construction and operation of these circuits willbe apparent from a description of one of the circuits 144a. The circuit1440 includes a control relay RLla arranged to be connected across thesecondary of transformer 140 through a normally opened contact 1CB1 thatis mechanically linked with the contacts of the main circuit breaker 36ain the module 34a so that when the contacts in 36a are closed, thecontacts 1CB1 are also closed to energize relay RLla. Relay RLla has anormally open contact lRLla and a normally closed contact ZRLIa (FIG. 3,designated by numeral 940 in FIG. 2). Closure of contact lRLIa energizestwo fan motors 148 (FIGS. 3 and 5) that are housed in the module packagefor the module 34a. Energization of motors 148 via contacts IRLla isthrough a current responsive element 150a that is physicallyincorporated in the circuit breaker 36a of the module 34a so that inresponse to excessive current through the element 1500 the circuitbreaker 36a is opened to disconnect the transformer 52a from the SCRcontroller 46. To this end, a normally open, temperature-responsivebimetal contact 152a is connected in series with a current limitingresistor 154a across the fan motors 148. Bimetal 152a is mounteddirectly on the heat sink for the diodes in the bridge rectifier 54a sothat in response to excessive temperature at the diode the bimetal 152acloses to parallel resistor 154a with motors 148 causing the currentthrough element 150a to increase to the point where it causes circuitbreaker 36a to open. As previously indicated in connection with thedescription of FIG. 2, the contacts 2RL1a (FIG. 3, designated 94a inFIG. 2) are normally closed but in response to energization of relayRLla contacts 2RLla open so that resistor 90a is inserted in series withthe current feedback from shunt to decrease the feedback applied acrossthe summing resistor 92. Similarly, should circuit breakers 36b or 360open due to excessive current through the input to the respectiveprimaries 114b, 1140, the corresponding contact 2RL1b or 2RL1c willclose to short the corresponding resistor b or 90 c to further increasethe current feedback to the summing resistor 92. In this regard, itshould be noted that each of the circuit breakers 36 includes at leasttwo current responsive elements (not shown) each of which is connectedin a different one of the input lines to the delta connected primary114, i.e., in series with a respective line, so that the current sensingelement opens the circuit breaker 36 in response to excessive current inany of the input phases to the transformer 52. Hence as indicatedearlier, if the circuit breaker 36 is opened, either due to manualpositioning of the circuit breaker or due to opening thereof in responseto excessive current in the primary 114a, a corresponding-resistor 90awill be shorted.

FIG. 3 also shows the specific construction of the wye-wye transformer59 through which the SCR firing circuit 58 is energized. Transformer 59is utilized to convert a three-wire input to a four-wire output with thefourth wire providing a false neutral in the SCR firing circuit 58. Theuse of the false neutral in the secondary of transformer 59 assures thatall six SCRs 110, 111 in the controller 46 fire in the desired sequenceindependent of phase rotation of the three-phase source 40.

Referring now in greater detail to the circuit diagram for thevoltage-current regulation circuit 62 illustrated in FIG. 4, the circuit62 is energized by the input at lines 132, 133 (FIGS. 3 and 4) from thestart-stop circuit (FIG. 3). The alternating current input is rectifiedat and the DC output from rectifier 170 is applied across a pair ofpotentiometers 172, 174 through a series regulator indicated generallyat 176 to provide a stable reference voltage across the potentiometers172, 174. Potentiometer 172 has a wiper 178 that serves as the currentreference source (98, FIG. 2), with wiper 178 being connected throughresistor 100 to the summing point 102. The summing point 102 is alsoconnected to the serially connected resistors 90a, 90b, 90c via the line180 to the output of the rectifier-filter circuit 88. As was previouslynoted, the current feedback signal from shunt 80 (through amplifier 82,chopper 84, amplifier 86 and rectifier and filter circuit 88, FIG. 1) isapplied in bucking relationship to the reference signal from wiper 178.Hence it will be apparent that for a positive increase in the DC outputcurrent across shunt 80, the feedback signal applied across summingresistor 92 increases in a negative direction. The output signaldeveloped across resistor 92 is applied to one-half of the NOR gatecircuit 72 which generally comprises a two-stage buffer amplifier formedby transistors 182, 183, the output of which drives the base of thetransistor 184.

Similarly, the potentiometer 174 has a wiper 185 that serves as thevoltage reference source (74, FIG. 2) to supply the voltage referencethrough resistor 76 to the summing point 70. The summing point 70 isalso connected through the resistor 66 and a suitable filter 186 to thenegative bus 48 via lead 188. For purposes of simplicity, filter 186 isomitted from FIG. 2 and it will be understood that filter 186 merelysmooths the ripples in the DC output developed across busses 48, 50 aswell as serving as a voltage divider to set the level of the voltagefeedback to the summing point 70. As indicated earlier, the voltagefeedback signal via resistor 66 bucks the reference voltage from wiper185 so that an increase in the voltage across busses 48, 50 results in anegatively increasing signal being applied to the summing point 70. Theoutput developed across resistor 68 is applied to the NOR gate 72through a buffer amplifier formed by two transistors 192, 193, theoutput of which drives the base of transistor 194. Transistors 184, 194have a common emitter-resistor 196 that develops a differential outputsignal in a manner to be described in greater detail. The output acrossresistor 196 is fed through an operational amplifier 200 to the controlinput 60 of the SCR firing circuit 58. As previously indicated, the SCRfiring circuit 58 may be of generally conventional construction. Inresponse to a variation in the level of the output signal developed atinput 60, corresponding equal shifts in the firing angle of all six SCRs110, 111 is achieved. In the preferred embodiment, the SCR firingcircuit was a Vectrol full-wave phasetrol," Model No. VPH1019-230/4603X3, heretofore sold commercially by the Sprague ElectricCompany, North Adams, Massachusetts. Amplifier 200 is primarily to matchthe output signal developed across resistor 196 with the firing circuit58 so that the firing angle of the SCRs 110, 111 can be varied oversubstantially. a full 175 degrees in response to the variationsdeveloped across output resistor 196.

The operation of the voltage-current regulation circuit 62 will bebetter understood assuming that there is initially no load on the sixSCRs 110, 111 and that the voltage reference at wiper 185 is set toregulate the DC output voltage at busses 48, 50 to 12 volts. Thereference voltage at wiper 185 is compared against the voltage feedbackvia line 188 which is initially zero at the. summing point 70. Hence thepositive reference causes the emitter-follower 1 92 to be forward biasedand this drives transistor 194 into conduction. The transistor 194 isone-half of the NOR gate 72 formed by transistors 184, 194. Transistor194 develops an output signal across resistor 196 which is fed toamplifier 200 to in turn develop a DC control signal at 60 which drivesthe SCR firing circuit. The magnitude of the signal at 60 varies theeffective width of the SCR gate pulses which, in turn, controls the SCRconduction angle. As the conduction angle of the six SCRs increases, themagnitude of the output voltage at 48, 50 will increase developing anincreasing feedback voltage across the output 48, 50 and this in turn isfed back via resistor 66 and compared at resistor 68 against the voltagereference from 185. The voltage feedback is negative relative to thepositive reference and hence when compared with the reference signal,the difference signal varies the base drive at transistor 194 toregulate the output at the constant 12 volts, regardless of line andload conditions. Regulation in a constant voltage mode continues untilthe amplified current feedback signal becomes large enough to turntransistor 184 on. In the absence of a load current or until the loadcurrent reaches a maximum value as determined by the setting of thecurrent reference wiper 178, the base of transistor 184 is reversebiased and transistor 184 remains off. As a result, only voltage controlis exercised by transistor 194. However, when the output current atbusses 48, 50 has reached a value which is sufficiently large that thefeedback from shunt 80 when compared with the current reference signalat wiper 178 turns transistor 184 on, conduction at transistor 184 turnstransistor 194 off via the common emitter resistor 196 and crossoverfrom voltage control to current control occurs. Further increases inoutput current result in a greater negative feedback that interacts withthe current reference signal at resistor 92 so that constant current ismaintained. During constant current con trol, the voltage is freetofall. Stated differently, when crossover from constant voltage controlto constant current control occurs, the SCRs are phased back to ashorter duration conduction angle so that current through the loadremains constant, even though more current is demanded. By the sametoken, when the device is in the constant voltage mode as opposed toconstant current, if the load were constant and the line or the loadwere to change such that the voltage tried to increase, the voltagewould be decreased.

As previously indicated, the current feedback is effected throughresistors a, 90b, 90, each of which is tied in with its respectivemodule 34a, 34b, 340; that is, the resistors 90a, 90b, 906 are arrangedto be shorted by respective contacts 2RL1a, 2RLlb,"2RLlc so that thefeedback level is inversely proportioned to the number of operativemodules. By way of further illustration, for a 21 module system, therewill be 21 resistors in series with the current feedback and eachresistor is shorted bya normally closed relay contact. When each moduleis energized by closing its associated circuit breaker 36, this, inturn, opens a normally closed relay contact 94, thereby inserting aresistor. As a result, the number of resistors that are active in thecurrent feedback network represent the number of modules that are' inoperation. In the event that a module 34 becomes inoperative as a resultof a failure mode or manual disconnect, this in turn reactivates a relaycontact 94 to short out the resistor 90 that represents that module inthe current feedback network- As a result, the current feedback signalis increased, thereby setting the automatic control to the point atwhich the full load current must be limited in order not to exceed thecapability of the remaining modules active in the system. This systemhas particular merit in a system capable of n modules 34 but where only2n/3 modules 34 are installed in the system, which leaves n/3 modulesthat are not operable at that time. The circuit breakers 36 for theassociated n/ 3 modules are left open. Using a normally closed relaycontact to shunt a resistor prevents exceeding the current capability ofthe remaining 2n/3 modules that are in the system. When other of the n/3modules are added and activated by closing their circuit breakers, thecontacts corresponding to contacts 94 are opened, thereby altering thecurrent feedback signal and allowing the system to deliver the fullcurrent capability as reflected by the increased number of modules. Thelevel of the current feedback will determine the maximum current outputat busses 48, 50, even though the wiper 178 is set for a greater currentthan the active modules are capable of producing.

The mechanical construction of the power supply 30 together with theconstruction of the individual modules 34 is better illustrated in FIGS.59 wherein a plurality of horizontally disposed U-shaped channels 210are mounted on vertical uprights 212. Each of the modules 34 has apairof bottom corner extrusions 214 having laterally outwardly projectingintegral flanges 216 slideable on the top face of an associated channel210. The flanges 216 and channels 210 extend the full length of themodules 34. Each of the bottom corner extrusions 214 are mounted onopposite ends of a pair of lower transformer brackets 217. Each bracket217 has a downturned flange on its outer end that is fastened on anupstanding leg 218 of the corner 214 by one of the screws 220.Similarly, upper comer extrusions 230 are mounted on opposite ends of apair of upper transformer brackets 232 by means of the upturned flangeson the ends of brackets that are screwed on downwardly depending legs234 of the upper comer extrusions 230. The laminations of the core 238of the transformer 52 are securely bolted together between the uppertransformer brackets 232 and the lower transformer brackets 217. Thetransformer primary winding 114 and secondary winding 116 are wound oncore 238 in a generally conventional manner. Hence the transformer andits mounting brackets 217, 232 rigidly support the corner extrusions214, 230, the lower corner extrusions 214 in turn providing a slideablemount on the channel 210 so that the modules 34 can slide outwardly fromthe frame members 212. The sides of the module 34 are each closed by avertical side panel 240 which is fastened on the integral legs 218, 234of the bottom and top comers 214, 230, respectively, by the fourtransformer mounting screws 220 and four additional screws 242. A flattop panel 246 is removably carried in grooves on the upper comerextrusion whereas a lower bottom panel 248' is removably carried ingrooves on the bottom corner extrusions 214. Front and rear grills 250,252, respectively, are mounted on opposite ends of the module 34 byscrews threaded in the corner extrusions. The mounting screws 242 at therear end of the modules 34, the right side as viewed in FIGS. and 6,also support a fan bracket 254 that carries the two fan motors 148 (FIG.3) for each of the modules 34.

The six diode rectifiers and the rectifying circuit 54 are mounted on asuitable heat sink 260 which in turn is mounted on a heat sink bracket262. Bracket 262 extends transversely of the module 34 and is fastenedat opposite lateral sides thereof to the bottom corner 214 by the lowerfront screws 242. The positive bus 48 and the negative bus 50 connectthe output of the rectifying circuit 54 to the main bus lines 48, 50with the busses 48', 50' extending from the rectifying circuit 54rearwardly through the module 34 and outwardly through one of the sidepanels 240 to suitable connectors at the rear of the modules where it isparalleled with the output from the other module 34.

The particular construction of a single module described hereinabove hasseveral important advantages. For purposes of illustration, the module34 described in connection with FIG. 5 is for a high voltage rectifiersystem utilizing the heat sink construction 260 illustrated in FIG. 5.Similarly, the output in a high voltage rectifying system may be byconventional high tension bus leads 48', 50. However, when the modularpower supply 30 is constructed for low voltage systems, many of the samestructural components can be used, namely, the comer extrusions 214,230, the same top panel 246, the same bottom panel 248, the front andrear grills 250, 252 and the fan bracket 254 and fan motors 148. Ingeneral, the principal difference then between a high voltage and lowvoltage module merely involves a different mounting arrangement for alow voltage, high current heat sink and a slightly different transformerthat is slightly larger but generally on the same order of dimensions asthe transformer illustrated in FIG. 5 for the high voltage system. Inthe preferred embodiment of a low voltage system, the side panels 240are modified so that the side panel serves not only as a structuralcomponent but also as a low voltage bus bar and, to some extent, servesto further conduct heat away from the low voltage heat sink.

It is also important that the various parts of each module are, to someextent, interchangeable. Hence the two bottom comers 214 have identicaltransverse cross sections and can be cut from the same extrusion.Similarly, the two upper corners 230 have identical transverse crosssections and are cut from the same extrusion. The top and bottom panels246, 248 are identical and the four transformer brackets 217, 232 areidentical. Although the front grill 250 is preferably of a differentconstruction than the rear grill 252, the front grill on a high voltagepower supply is interchangeable with the front grill on a low voltagepower supply. Additionally, the modules 34 for either a high voltageapplication or a low voltage application have the same outsidedimensions.

As noted hereinabove, the transformer brackets 232, 217 extendtransversely substantially the full width of the module 34 and provide amain structural component giving rigidity to the module. Hence in thepreferred embodiment, the transformer brackets 232, 217 are made ofheavy guage steel whereas the comers 214, 230 are extruded aluminum andthe top, bottom and side panels are aluminum sheet metal. The grills250, 252 are molded plastic. Hence the majority of the weight of anindividual module is in the core 238 and the windings 114, 116. At leastas important is the fact that each individual module 34 can be removedfrom the power supply 30 so that the modules can be handled, transportedand installed individually to complete the assembly on site. This hasnumerous advantages over a bulky, heavy power supply providing the samekva output and contained in a single package. By way of example, a 24volt module weighs approximately 234 pounds and a frame for 21 modulesweighs approximately 2,500 pounds, whereasfor a high voltage system at300 volts utilizes modules each weighing 225 pounds with a 21 moduleframe weighing approximately 2,450 pounds.

The control circuitry described in connection with FIGS. l-4 achieveseffective control of plural modules made under close productiontolerances to provide mechanical and electrical uniformity as betweendifferent modules. Similarly, the construction described hereinabove canprovide mechanical and electrical symmetry in the different phases of anindividual module. In this regard, the reactance of the transformer 52is the most single important factor in determining how the current isshared as between parallel modules as well as between diodes within therectifying circuit 54 of a given module. Hence variations due-todifferences between diodes and the rectifying circuits 54 are ofsecondary importance as compared to the transformer 52.

The horizontal air flow pattern through each of the individual modulesalso offers several distinct advantages, including a relatively largeinlet at the front grill 250 for each individual module as well as alarge combined total area for all of the modules when assembled in abank such as the 21 module bank shown in FIG. 1. The cooling air isdrawn by the fans located at the rear of the module so that the cool airfirst cools the heat sinks, such as the heat sink 260, and then thetransformers before being exhausted at the rear of the module to grill252. Again each of the individual grills on a single module offers arelatively large exhaust area as well as a combined exhaust area for theplurality of modules assembled in a bank. The flow from frontto rear, ascontrasted to vertical flow means that the cooling air is likely to becleaner as contrasted to a system having an inlet at only a low leveladjacent the floor. With a rear exhaust, it is not necessary to have asubstantial clearance at the top of the power supply 30. Also with thelarge inlet and outlet areas for the cooling air, large quantities ofair can be moved at a relatively low velocity, producing a much quieteroperating system by comparison to prior art devices.

Other important advantages of the modular power supply describedhereinabove are that a complete power supply can be built up frominventory modules to meet practically any power requirement by using theproper number of modules. A customer anticipating large future powerrequirements need not purchase the entire power supply to service thosefuture requirements but by buying a large cabinet and using less thanthe maximum number of modules, the customer can meet present powerrequirements and then add additional modules as his demands increase.The system is very reliable in that extra modules may be kept on hand bythe customer to eliminate down time in the event of a failure at one ofthe modules. The defective module is merely left in place and itscircuit breaker opened while the circuit breaker on the spare module isclosed. A self-adjusting voltage and current control with current limitoverride' according to the number of modules in operation, and indeedthe particular modules that are active, facilitate this flexibility andreliability of the modular power supply.

By way of further disclosure, the total capacity of the modular powersupply 30 of the type described hereinabove is determined primarily bythe ratings of the SCRs 110, 111 in the SCR controller. The ratings onair cooled SCRs presently available commercially are such that, in thepreferred embodiment, the total kw. output from the power supply 30 ison the order of 500 kw. After extensive development, it has been foundthat the above total kw. output can be achieved while maintainingadequate safety ranges. Moreover, it has been found by extensivedevelopment that the above maximum output capabilities can be achievedmost effectively by using 28 separate modules 34, for example, fourvertical columns of seven modules per column. This particulararrangement provides a very compactpower supply having a large ultimatepower capability.

Referring again to the drawings, FIGS. -13 show a modified module 34'for use with high current, low voltage power supplies. It will beapparent that the overall mechanical arrangement of the modified module34' is substantially similar in many respects to the high voltage, lowcurrent module 34 with substantially identical components beingdesignated by identical reference numerals followed by a prime." Moreparticularly, the low voltage module 34 includes a pair of bottom comerextrusions 214, each of which has an upstanding leg 218', a laterallyoutwardly projecting flange 216' and a bottom flange 219. Flange 216' isadapted to slideably support the module 34 on the U-shaped channels 210so that the module can be removed from the framing 212. The bottomflange 219 is notchedto receive the bottom panel 248. Similarly, theupper corner extrusion 230' includes a downwardly depending leg 234 anda laterally inwardly projecting flange 235" that is grooved to receivethe top panel.

246. The rigid rectangular orientation of the corners 214, 230 ismaintained by the pair of rigid upper transformer brackets 232' thatextend transversely of the module 34' and are fastened at their oppositeends on the respective upper comer extrusions 230 by screws 220'.Similarly, the lower pair of transformer brackets 217' extendtransversely the full width of the module 34' are fastened at theiropposite ends to the upstanding legs 218 of the lowerlcorner extrusions214 by the screws 220'. The transformer brackets 217', 232 support thetransformer core 238 on which the low voltage windings 114', 116' arewound. The rear end of module 34 is closed by a molded plastic grill 252and the front end of module 34 is closed by the front grill 250.

Although it will be understood that the transformer comprising a core238 and windings 114, 116 will differ slightly for low voltageapplications as compared to high voltage applications, the difference isnot substantial. Hence the principal difference between the modules 34(FIG. 5) and 34 (FIGS. 10-13) is in the construction of the side panelscorrespond ing to the side panel 240 (FIG. 5). More particularly, eachside of the module 34' comprises a heavy extruded aluminum bus bar 300that is grooved longitudinally along its upper edge to interlock with anelongated insulating spacer 302, and similarly is grooved longitudinallyalong its lower edge to interlock with the elongated insulating spacer304. With the spacers 302, 304 engaged on the bus bar 300, the overallheight of the assembled panel for the module 34' is the same as theoverall height for the side panel 240 (FIG. 6). Hence the outsidedimensions of the module 34 are substantially identical to the outsidedimensions of the module 34 (FIG. 5) so that the modules fit in the samespace in the cabinet including uprights 212. With the low voltage module34', substantially larger heat sinks 260 are required to dissipateadditional heat generated by the low voltage rectifying circuit. The lowvoltage heat sink has a pair of out-turned mounting flanges which arebolted directly on the front end of bus bar 300 by four screws 308. Thescrews 220' and 242' retain the side panel assembly including spacerstrips 302, 304 and bus bar 300 on the upper. and lower cornerextrusions 230', 214. It should be noted that the out-turned mountingflanges 307 on the heat sink 260' provide a direct electrical connectionbetween the diode rectifiers in the rectifying circuit and the bus bar300. Additionally, the bus bars 300 support the respective heat sinks260' and provide an electrical connection from the rectifying circuitscorresponding to rectifying circuit 54 (FIG. 3). The construction of theleft side of the module 34 as viewed in FIG. 13 is substantiallyidentical to the construction of the right side described hereinaboveand better illustrated in FIGS. 1113. Additionally, it should be notedthat bus bar 300 extends the full length of the module 34' and isprovided with mounting holes 312 for assembly on the main DC bus baroutput.

As with the module 34 (FIG. 5), the construction of the module 34'allows for substantial interchangeability of parts, not only within themodule but also interchangeability with the module 34'. Although thelocation of the mounting holes for the screws 220, 242 that hold theside panel 240 (FIGS. 58) in place is slightly different from thecorresponding mounting holes in the module 34' (FIG. l0l3), substantialsavings are realized because the comers 230, 230' are made from the sameextrusions as are the lower corners 214, 214.

We claim:

1. A modular power supply for use in an alternating to direct currentconverter having a plurality of modules mounted in a frame, said powersupply comprising a housing that extends longitudinally in a horizontaldirection and has a transverse vertical cross section that is generallyrectangular, said housing having an inlet at one end thereof and anoutlet at the other end, said housing further having a substantiallyclosed top wall, a substantially closed bottom wall and substantiallyclosed sidewalls so as to define a confining channel for circulatingcooling fluid through said housing, fan means mounted in said housingand adapted. to establish a current of moving air through said housingfrom the inlet thereof to the outlet, and electrical rectifyingcomponents mounted in said housing, and wherein said housing includes apair of bottom comer extrusions, each of which has an upstanding legthat extends longitudinally of the housing substantially the full depththereof and has a respective sidewall mounted thereon, a bottom flangeon each comer extrusion integral with its respective corner leg andextending laterally inwardly toward the opposite corner extrusion, saidbottom flanges extending longitudinally of said housing forsubstantially the full depth of said module, said bottom wall beingmounted on said bottom flanges and a lateral flange integral with eachcorner extrusion and projecting laterally outwardly therefrom andextending substantially the full depth of said module and arranged tosiideably mount said housing on said converter frame whereby saidhousing may be slid out of said converter by sliding engagement betweensaid converter frame and said lateral flanges.

2. The power supply set forth in claim 1 wherein said housing furthercomprises a pair of upper corner extrusions each of which is disposed atan opposite side of said housing and extends substantially the fulldepth of said module, each of said comer extrusions having an upper armportion that projects laterally inwardly of said housing toward theopposite upper comer extrusion and a downwardly depending arm which isadapted to receive a side panel of said module, and wherein said topwall is mounted on said upper arm portions and said sidewalls aremounted on said downwardly depending arms.

3. The power supply set forth in claim 2 wherein said lower comerextrusions have identical transverse cross sections.

4. The power supply set forth in claim 3 wherein said upper comerextrusions have substantially identical transverse cross sections.

5. The power supply set forth in claim 2 wherein said upper comerextrusions have substantially identical transverse cross sections.

6. The power supply set forth in claim 1 wherein said sidewalls eachcomprise a single sheet.

7. The power supply set forth in claim 1 wherein said top wall and saidbottom wall each comprise substantially identical single pieces of flatsheet material.

8. The power supply set forth in-claim 1 wherein said lower flanges onsaid bottom extrusions are each provided with a horizontal groove thatextends longitudinally substantially the full length of said cornerextrusions, and wherein said bottom wall comprises a single piece offlat sheet material slideably engaged at its laterally outer edges inthe groove on the opposite lower comer extrusions.

9. The power supply set forth in claim 1 wherein each of said sidewallscomprises an elongated metallic bus bar extending substantially the fulldepth of the housing, said power supply further comprises a heat sinkmounted directly on said bus bar so as to provide thermal and electricalconducting paths between said heat sink and said bus bar.

10. The power supply set forth in claim 9 wherein means are provided onsaid bus bar for attaching said bus bar to an electrical output bus.

1]. The power supply set forth in claim 10 wherein said heat sink ismounted on said bus bar adjacent one end thereof and said bus outputmounting means are located on said bus bar adjacent the opposite end ofsaid bus bar.

12. The power supply set forth in claim 1 wherein a transformer ismounted in said housing by at least a pair of mounting brackets thatextend transversely of said housing substantially the full width of saidhousing, an upper one of said transformer brackets is fastened at oneend thereof to one sidewall of said housing and the opposite end of saidbracket is fastened at the opposite sidewall of said housing, andwherein said brackets are made of rigid material to impart rigidity tosaid housing.

13. The power supply set forth in claim 12 wherein said housingcomprises a pair of upper corner extrusions extending substantially thefull length of said housing and wherein one of said transformer bracketsis fastened at opposite ends to opposite upper corner extrusions.

14. A modular power supply for use in an alternating to direct currentconverter comprising an elongated housing having a generally rectangulartransverse cross section and defining an air flow path therethrough froman inlet end thereof to an outlet end thereof, said housing comprisingat least an upper corner extrusion and a lower corner extrusion, saidupper extrusion having a downwardly depending leg, and said lower cornerextrusion having an upwardly depending leg, said legs extendingsubstantially the full length of said module, and a side panel mountedon said legs to close the sidewall of said module, said housing furtherhaving electrical rectifying components mounted therein and disposed inthe path of cooling air through said housing.

15. The modular housing set forth in claim 14 wherein said sidewallcomprises a bus bar formed of electrically conducting material andextending it longitudinally of the housing, a heat sink for saidrectifying components mounted in thermal and electrical conductingrelation on said bus bar, and means on said bus bar remote from saidheat sink for attaching said bus bar to an electrical output bus,

1. A modular power supply for use in an alternating to direct currentconverter having a plurality of modules mounted in a frame, said powersupply comprising a housing that extends longitudinally in a horizontaldirection and has a transverse vertical cross section that is generallyrectangular, said housing having an inlet at one end thereof and anoutlet at the other end, said housing further having a substantiallyclosed top wall, a substantially closed bottom wall and substantiallyclosed sidewalls so as to define a confining channel for circulatingcooling fluid through said housing, fan means mounted in said housingand adapted to establish a current of moving air through said housingfrom the inlet thereof to the outlet, and electrical rectifyingcomponents mounted in said housing, and wherein said housing includes apair of bottom corner extrusions, each of which has an upstanding legthat extends longitudinally of the housing substantially the full depththereof and has a respective sidewall mounted thereon, a bottom flangeon each corner extrusion integral with its respective corner leg andextending laterally inwardly toward the opposite corner extrusion, saidbottom flanges extending longitudinally of said housing forsubstantially the full depth of said module, said bottom wall beingmounted on said bottom flanges and a lateral flange integral with eachcorner extrusion and projecting laterally outwardly therefrom Andextending substantially the full depth of said module and arranged toslideably mount said housing on said converter frame whereby saidhousing may be slid out of said converter by sliding engagement betweensaid converter frame and said lateral flanges.
 2. The power supply setforth in claim 1 wherein said housing further comprises a pair of uppercorner extrusions each of which is disposed at an opposite side of saidhousing and extends substantially the full depth of said module, each ofsaid corner extrusions having an upper arm portion that projectslaterally inwardly of said housing toward the opposite upper cornerextrusion and a downwardly depending arm which is adapted to receive aside panel of said module, and wherein said top wall is mounted on saidupper arm portions and said sidewalls are mounted on said downwardlydepending arms.
 3. The power supply set forth in claim 2 wherein saidlower corner extrusions have identical transverse cross sections.
 4. Thepower supply set forth in claim 3 wherein said upper corner extrusionshave substantially identical transverse cross sections.
 5. The powersupply set forth in claim 2 wherein said upper corner extrusions havesubstantially identical transverse cross sections.
 6. The power supplyset forth in claim 1 wherein said sidewalls each comprise a singlesheet.
 7. The power supply set forth in claim 1 wherein said top walland said bottom wall each comprise substantially identical single piecesof flat sheet material.
 8. The power supply set forth in claim 1 whereinsaid lower flanges on said bottom extrusions are each provided with ahorizontal groove that extends longitudinally substantially the fulllength of said corner extrusions, and wherein said bottom wall comprisesa single piece of flat sheet material slideably engaged at its laterallyouter edges in the groove on the opposite lower corner extrusions. 9.The power supply set forth in claim 1 wherein each of said sidewallscomprises an elongated metallic bus bar extending substantially the fulldepth of the housing, said power supply further comprises a heat sinkmounted directly on said bus bar so as to provide thermal and electricalconducting paths between said heat sink and said bus bar.
 10. The powersupply set forth in claim 9 wherein means are provided on said bus barfor attaching said bus bar to an electrical output bus.
 11. The powersupply set forth in claim 10 wherein said heat sink is mounted on saidbus bar adjacent one end thereof and said bus output mounting means arelocated on said bus bar adjacent the opposite end of said bus bar. 12.The power supply set forth in claim 1 wherein a transformer is mountedin said housing by at least a pair of mounting brackets that extendtransversely of said housing substantially the full width of saidhousing, an upper one of said transformer brackets is fastened at oneend thereof to one sidewall of said housing and the opposite end of saidbracket is fastened at the opposite sidewall of said housing, andwherein said brackets are made of rigid material to impart rigidity tosaid housing.
 13. The power supply set forth in claim 12 wherein saidhousing comprises a pair of upper corner extrusions extendingsubstantially the full length of said housing and wherein one of saidtransformer brackets is fastened at opposite ends to opposite uppercorner extrusions.
 14. A modular power supply for use in an alternatingto direct current converter comprising an elongated housing having agenerally rectangular transverse cross section and defining an air flowpath therethrough from an inlet end thereof to an outlet end thereof,said housing comprising at least an upper corner extrusion and a lowercorner extrusion, said upper extrusion having a downwardly dependingleg, and said lower corner extrusion having an upwardly depending leg,said legs extending substantially the full length of said module, and aside panel mounted on said legs to close the sidewall of said mOdule,said housing further having electrical rectifying components mountedtherein and disposed in the path of cooling air through said housing.15. The modular housing set forth in claim 14 wherein said sidewallcomprises a bus bar formed of electrically conducting material andextending it longitudinally of the housing, a heat sink for saidrectifying components mounted in thermal and electrical conductingrelation on said bus bar, and means on said bus bar remote from saidheat sink for attaching said bus bar to an electrical output bus.